Finite Element Analysis Of H-shaped Mandibular Defect Reconstruction By Different Fibula Folding And Internal Fixation Methods

Objective: We investigated the biomechanical rules of different fibula folding and internal fixation methods for the reconstruction of mandibular H-shaped defects by three-dimensional finite element method,compared the biomechanical characteristics of different surgical methods,provided mechanical data for the clinical design of surgical plans,and explored the superior method for the reconstruction of mandibular H-shaped defects by folding fibula flap from the mechanical point of view.Methods: A healthy adult male volunteer from Kunming Medical University was selected to undergo CT scan of the mandible and fibula.Import the data into Mimics 19.0 to reconstruct the normal mandible and fibula three-dimensional model,and then import the model into Geomagic Studio 2013,Proplan CMF 3.0,Solid Works2017 and other software for processing,and establish a normal mandible and folded fibula to reconstruct the mandible H-type defect(a semilateral mandible defect that does not cross the midline of the mandible,including the condylar process)finite element model.On the basis of the folded fibular flap model,the finite element model of the reconstructed mandible using simple small titanium plate fixation and reconstruction plate plus small titanium plate fixation was established.The normal mandible and four sets of reconstructed mandible models were imported into Ansys software to analyze the biomechanical characteristics of the folded fibular flap by finite element method.Results: 1.a finite element model of the normal mandible was successfully established,based on which four groups of finite element models with different folding and internal fixation methods were established for the reconstruction of H-shaped mandibular defects with folded fibula flaps.2.under the same load,the stress concentration areas of the normal mandible were the junction between the neck of the condyle,the mandibular angle,the teeth,the mandibular body and the ascending branch on both sides,with the maximum stress at the mandibular angle being 42.36 MPa.The maximum stress in the mandibular model after fibula reconstruction was also located at the mandibular angle in four groups,among which the maximum stress in model C(inferior folding small titanium plate group)was73.695 MPa,an increase of 72.2% compared with the normal mandible.3.The maximum stress in the titanium plate was located in the small titanium plate in the folding part of the mandible and fibula in model A(superior folding small titanium plate group),with a size of 170.45 MPa,while the stress in the rest of the titanium plate was much smaller than this value.4.The stress value of the first titanium nail near the broken end of all four groups of models was larger than that of the other titanium nails,and the maximum value was located at the first titanium nail at the lower end of the junction of the fibula and mandible in model B(up-folded reconstructed plate group),with a size of 46.751 MPa.5.The up-folded group(model AB)had greater stress and strain at fibula section 1 compared to the down-folded group(model CD),and the stress and strain at the stress and strain were smaller at fibular section 2,but the displacement was smaller at both sections.6.From the stress and strain clouds of fibular section 1 of the four groups of models,it can be seen that the stresses were mainly concentrated in the non-folded part of the fibular break,and the stresses at the break of the folded fibular flap were much smaller than those in the non-folded part.Conclusions: 1.From the perspective of mechanics,the upwardly folded fibular flap is used to reconstruct the H-shaped defect of the mandible flap,which has less displacement at the broken end of the bone,better initial stability,and is more conducive to the healing of the bone flap,which is a better method for reconstructing the H-shaped defect of the mandible.2.When the H-type defect of the mandible is repaired by folding fibular flap,whether it is fixed by small titanium plate or small titanium plate plus reconstruction plate,the maximum local stress of titanium plate and titanium nail is much smaller than the limit value that may occur titanium plate breaking and titanium nail loosening,so from a mechanical point of view,both fixing methods can meet the needs of surgical treatment.